Offshore platforms and method of installing same



Oct. 11, 1966 c. J. FOSTER OFFSHORE PLATFORMS AND METHOD OF INSTALLINGSAME Filed Nov. 26. 1965 INVENTOR:

CHE/S TOP/ ER J F0372? United States Patent 3,277,653 OFFSHORE PLATFORMSAND METHOD OF INSTALLING SAME Christopher J. Foster, 44 Whitehall St.,Sands Point, N .Y. Filed Nov. 26, 1963, Ser. No. 326,159 4 Claims. (Cl.61-465) This application is a continuation-in-part of copendingapplication Serial No. 680,119, filed August 26, 1957, now abandoned.

This invention relates to relocatable offshore platforms as may be usedto support apparatus for drilling oil wells beneath coastal waters. Moreparticularly the invention relates to techniques for temporarilyanchoring such platforms in a manner providing improved stability, andproviding high load supporting capability and firm anchorage of-theplatform legs which typically extend downward to the ocean bed.

The invention is especially useful where the platform is to be situatedin comparatively deep water over a bottom of soft mud or silt ofconsiderable dept-h. For example, at some Mississippi River delta sitesunder which it is believed that oil is to be found, the water may befrom 150 to 300 feet deep and the bottom of the sea consists essentiallyof alluvial soil or soft mud having a depth of from 75 to 150 feetoverlying a sub-bottom o-f firm sand or the like. The mud layer has aload bearing capacity of only about 200 pounds per square foot, whereasthe underlying sandy bottom has much greater load bearing capability.Moreover, the sunface of the mud bottom, as well as that of thesub-bottom, may not always be level but may slope or be irregular.

Under these and other working conditions, those offshore platforms ofthe past which for their support rely upon broad based footing or sunkenplatforms or the like, which rest upon the surface of the ocean bottom,are inadequate. Their load carrying capability is limited, as apractical matter, by the total load supporting area as is provided bythe footing or sunken platform, an unduly large area being required tosupport any substantial load where the soil pressure is only about 200pounds per square foot. In addition, their general overall stability,and their ability to withstand high wave and wind pressures may beseriously impaired where the mud bottom surface is uneven, or where themud bottom itself does not have uniform soil pressure throughout thesupport area.

Accordingly, the present invention contemplates a method and means fordriving the legs of such a platform completely through the mud layer,and to firm but but releasable support within the sub-bottom, withoutthe use of secondary pile driving equipment, and in a manner as willprecondition the legs to withstand not only the intended platform loadbut also the very high and comparatively momentary-applied forces as areproduced by other factors such as wave and wind action, ramming or thelike. Heretofore it has not been understood how, without the use ofsecondary apparatus, an offshore platform of the temporary andrelocatable type might be itself adapted and used to set its own legs ina manner achieving these results.

Briefly and generally describing the invention in its preferred form,the working platform, which is rigid and nonfioatable, is supported by atripod arrangement of three laterally spaced apart vertical legs orpylons, as they will be referred to herein. The pylons are hollow andhave valves or the like to admit sea Water for sinking them into theirinitial positions, and each pylon is mounted for slidable movementthrough the working platform independently of each other so that eachmay be separately driven to a common soil-bearing resistance value whichmay vary between the pylon locations. Of

course, in view of the great overall height of the pylons as will berequired to attain the intended support depth, each pylon is formed byattachable sections of a uniform and convenient length. However, and fora purpose as will be described, the height of each pylon at virtuallyall times after the initial sinking operation and during the subsequentplacement operation is maintained at about seventy-five feet above sealevel.

In addition to the working platform and pylons, the offshore platformassembly includes three hollow and buoyant tanks, each in surroundingand unattached slidable relation with one of the respective pylons,which not only serve to float the assembly while being towed to thedrill site but also become a part of the platform supporting structureafter the pylons have been set, as will be seen. The three tanks arerigidly attached to each other in their laterally spaced apartrelationship by a network of welded pipe adequate for the purpose.However, since it is desirable that the Working platform be ultimatelysituated some fifty feet above sea level so as to avoid direct impactingof the highest waves thereon, the invention contemplates that the pipeframework will be disposed above the buoyant tanks, and will extend inheight between the tanks and the working platform to support the latterat its desired fifty foot elevation both when he assembly is being towedto the site and subsequently during the pylon placement operation. Thus,the present invention eliminates the necessity for including hydraulicor other jacks to hoist the working platform to its ultimately desiredheight on the pylons.

Rather than by a conventional pile driving or similar driving technique,the present invention contemplates a pressing of the pylons through themud layer and into the sub-bottom until the desired high resistancevalue has been attained. The technique utilizes the total weight of theoffshore platform assembly plus an additional weight of sea water forthe purpose. Thus, after the pylons have been sunk to their initialpositions against the ocean floor, the aforementioned overheights of thepylons are filled with additional sea Water ballast so as to increasetheir respective effective weights (and also to increase their internalpressure to resist buckling or the like during the pressing operation),and the buoyant tank structure is attached to the Working platform. Theplatform is attached to the pylons by separate ratchet and pawlarrangements at each pylon and sea Water is alternately admitted to andpumped from the buoyant tanks to impose further pressing action on thepylons. That is, the sinking force of the tanks, which are at leastpartially filled with sea water, is ultimately transmit-ted to thepylons for a period of time to press them a desired unit distancedownwardly. The force is then completely removed by expelling the waterfrom the tanks and by the automatic detaching of the platform from thepylons as is effected by the ratchet and pawl arrangements. The tanksare thus refioated so as to retraverse the unit distance, whereupon theattaching of the platform to the pylons, and the filling and partialsinking of the tanks is repeated to press the pylons another unitdistance. In view of the independent operation of the respectiveratchets and pawls it is apparent that, except as limited by any bendingmoment established in the pylon, the total load of all of the tanks maybe transmitted to only one pylon as may be found necessary at any stageof the pressing operation to achieve equal soil resistance at all of thepylons. It also becomes apparent that, by reason of the chain ofattachments between the tanks and the pylons, the weight of the Workingplatform itself, including that of all of the drilling and otherequipment as may then be situated thereon, is also transmitted to thepylons. Thus, the sinking tanks pull the working platform downwardly theaforementioned unit distance and, by the ratchet and pawl connections,the platform presses the pylons downwardly. As the tanks are alternatelyrefloated, the ratchet and pawl arrangement permits the working platformto elevate itself with respect to the pylons as it is carried upwardlyby the rising tanks. Of course, pylon sections are attached asnecessary, and additional ballast water is pumped into the pylons asaforesaid, as the pressing operation proceeds.

The invention contemplates that, considering the total weight of thepylons and working platform (with its drilling and other equipment) asbeing the normal load to be supported, each pylon will be pressed to adepth whereat the soil resistance value is about three times that whichit may be normally expected to support. That is, during the pylonpressing operation, each pylon will have sustained an overload of abouttwo hundred percent. To make this excess support capability of thepylons available to resist wave and other momentary forces as aforesaid,the invention further contemplates that the placement load will berelieved to this extent after the pressing operation has been completed.This is accomplished by emptying the aforementioned excess ballast waterfrom the pylon overheight and, in fact and if desired, by additionallyemptying some of the normal ballast water from within the pylons tobelow sea level. In addition, the buoyant tanks and their connectingframework are disconnected from the work-ing platform which then remainssupported solely by the pylons, the tanks being filled with water andpermitted to sink to the ocean floor.

By reason of their height and surrounding relationship with the pylonsas the connected tanks lie on the ocean floor, it will be noted that thepylons are thereby laterally braced at or somewhat near their middlelengths, considering that the pylons extend considerably below the oceanbottom.

Each pylon has a plain and spherically shaped closed lower end, and isvoid of lateral pro-tuberances such as tank type footings or the like. Aspherical, rather than a hat or pointed lower end is believed to themore effective in the pressing operating by reason of both its shape andits inherent strength, and in the subsequent operation of lifting thepylons when the offshore platform assembly is to be towed to a newlocation.

To remove the offshore platform installation to a new location, thethree sunken tanks are pumped free of the water which they contain sothat they rise, sliding upwardly along the submerged length of thepylons, into contact with the work-ing platform to support the same andrelieve its weight from the pylons. The ratchet and pawl arrangements,by which the weight of the working platform was distributed to therespective pylons, are then disconnected so that, while stillsurrounding the same, the tanks and working platform are completelydisconnected from the pylons. The pylons are then pumped free of theircontained water so that their buoyancy will draw them upwardly out oftheir situation within the ocean bottom. The pylon sections aredisconnected as the pylons rise, thereby additionally decreasing theirweight. If necessary, the ratchet and pawl arrangements at each pylonmay be of a reversible type so that the force of buoyancy of the buoyanttanks may be exerted on any or all of the pylons to overcome suctionforces and otherwise assist in their upward removal.

These and other objects, features and advantages of the presentinvention will become more fully apparent from the following detaileddescription thereof, when taken together with the accompanying drawingsin which:

FIGURE 1 is an elevational showing of an offshore platform assembly inaccordance with the present invention as it would appear when floating,as while being towed to an offshore drilling site;

FIGURE 2 is a plan view of the offshore platform assembly to furtherillustrate its overall arrangement;

FIGURE 3 is an elevational showing of the platform assembly as it wouldappear during the pylon sinking and pressing operations or,alternatively, during the removal of the pylons from the ocean bottom;

FIGURE 4 is another elevational showing of the platform assembly as itwould appear when fully installed and ready for its intended use;

FIGURE 5 is an enlarged and fragmentary showing of the details of theratchet and pawl connection between the working platform and the pylonsof the offshore platform assembly; and

FIGURE 6 is an enlarged and fragmentary showing of the details of thetemporary connection between the working platform and the buoyant tankarrangement the-rebelow, as is also included in the offshore platformassembly of the present invention.

Referring to FIGURES 1-4 of the drawings, an offshore platform assemblyin accordance with the invention includes a working platform 1 which isinitially supported by the three buoyant tanks 2 and their associatedattaching framework structure 11 when the assembly is in floatingcondition as illustrated by FIGURE 1, and which will be subsequentlysupported by the three pylons 5 when the assembly has been installed asillustrated by FIGURE 4.

The working platform 1 is of rigid and non-floatable construction forsupporting an oil well drilling derrick as is generally indicated byreference numeral 12. As indicated in FIGURES 2 and 4, the drillingderrick 12 is situated above a rectangular-shaped side out 13 of theplatform 1, and supports a Christmas tree".type drilling apparatus whichincludes a diagonal brace arrangement 15, a vertical central pipe 14having a pipe end extension 16 connected thereto by a universal joint 30for pivotal movement as indicated by dotted lines in FIGURE 4. A sphericanchor buoy 17 is slidably mounted on the pipe end extension 16 forindicating the well location after the offshore platform assembly of thepresent invention has been removed. The buoy 17 is anchored to the oceanbottom, as indicated by anchor chains 18, to prevent excessive strainson the pipe 14.

The elongated and cylindrical pylons 5 are slideable with respect to theworking platform 1 through the respective circular platform openings 4in which they are mounted in suitable diameter conforming relation.However, and referring to FIGURE 2, at three equally spaced apartlocations about the periphery of each pylon 5 and platform opening 4there is a ratchet and pawl arrangement, generally indicated byreference numeral 32, for transmitting the weight of the workingplatform 1 to the respective pylons 5 when the normal working load iswholly supported by the latter as indicated in FIGURE 4. Theconstruction of each ratchet and pawl arrangement 32 is illustrated byFIGURE 5 wherein it is shown that a vertical ladder 6 having spacedapart rungs 7 is attached along the length of the pylon 5, such beingattached at each of the three peripherally spaced locations on the pylonas aforesaid. A pawl 8 is pivotally attached by a pivot shaft 9 to theworking platform 1 at each of the corresponding locations at thecircular platform opening 4, each of the pawls 8 being biased by aspring 10 so that its lower end projects radially towards the center ofthe opening 4 and into engagement with the adjacent rung 7 of the pylonladder 6. As will later be more fully understood, during the pylonpressing operation the platform 1 and pylon 5 will concurrently move indownward direction, during which movement each of the pawls 8 will be inengagement with one of the rungs 7 as shown in FIGURE 5, and thereafterthe platform 1 will be moved upwardly with respect to the pylon 5 in themanner indicated by dotted lines in the same figure for engagement withthe next higher rung 7 as shown, during which subsequent upward movementof the platform the pawl 8 will be deflected and pivoted by the nexthigher rung so that the latter may become properly engaged by the pawlfor a subsequent and concurrent downward movement of the platform andpylon.

After the drilling operation is completed and the pylons 5 are to belifted from the ocean bottom 19, 20, all of the pawls 8 are pivoted,either manually or otherwise, against the bias of their respectivesprings 10, and held out of engagement with any of the rungs 7 so as topermit the associated pylon to slide upwardly relative to theplatform 1. Should it be necessary to exert upward pull on the pylon aswill be explained, the pawls 8 may either be inverted or otherwise be ofa reversible type for engaging the underside of one of the rungs 7,rather than the upperside as illustrated, whereby upward movement of theplatform 1 will exert the requisite upward pull on the pylon 5.

The pylons 5 themselves are of hollow tubular construction, being formedof attachable ring-shaped sections 5a of convenient unit length asindicated only in FIGURE 1, any number thereof being used as required toform the total length of the pylon 5. The lowermost section has aspherical shaped closed end as indicated by reference numeral 5b. Eachpylon has a uniform diameter of feet throughout its length, and it isbelieved that the spherical shape at the lower end thereof is best forease of penetration of, and withdrawal from the ocean bottom, and forresistance to crushing forces as may be encountered.

Referring now to the buoyant tanks 2, each has heavy weight and is ofhollow, totally enclosed and circular construction so as to befioatable. Each tank 2 has a central, cylindrically shaped opening 20(FIGURE 1) therethrough for slidable passage of one of the pylons 5.Considering the diameter of each pylon to be 20 feet, each tank 2 shouldhave an outside diameter of about 80 feet and overall height of about 28feet. All of the tanks 2 are rigidly attached together by a welded pipesuperstructure or framework 11, and it will be noted that thistruss-like framework has considerable height to support the platform 1some 50 feet above sea level when the offshore platform assembly is infloated condition as illustrated in FIGURE 1. Thus, the platform 1 is atall times supported at an elevation high enough to avoid impact by evengiant waves, of some 30 to feet in height, as might be experiencedduring hurricane weather.

At a number of spaced apart locations along its upper end, the framework11 is bolted to the platform 1 in a detachable arrangement, as generallyindicated by reference numeral 31, the details of each such attachmentbeing illustrated in FIGURE 6. As shown in the latter figure, thereleasable attachment includes a plate 23 which is rigidly secured tothe framework 11, and to which the platform 1 is releasably attached, asby bolts 22.

Both the hollow pylons 5 and the hollow tanks 2 are provided withsuitable valve openings (not shown) and suitable water pumping orcompressed air connections (not shown) which are operable from theplatform 1 to either admit sea water thereinto, or empty the sea watertherefrom as desired at the hereinafter described appropriate times.

Before describing the self-installing and self-removal operations of theoffshore platform assembly, it should be noted that at least during thepylon pressing operation each pylon should include suflicient pylonsections 5a to provide an overheight, generally indicated by referencenumeral 36 (FIGURE 3), for containing additional ballast water to aheight of about 75 feet above sea level for a purpose to be described.

Referring now to the operation of the offshore platform assembly wherebyeach of the pylons 5 is pressed through the mud layer 19 and into thefirm sub-bottom 20 of the ocean floor, the assembly is towed to thedrill site in its floating condition as shown in FIGURE 1. Although theillustration shows the lower ends 5b of the pylons 5 as then beingsubstantially within the cylindrical openings 2:: of the respectivetanks 2, it is preferable to permit the pylons to project some 30 feetbelow the tank bottoms when the assembly is being towed over deep water.At this time the platform 1 is preferably attached by the releasableattachments 31 to the tank framework 11, although it need not be sincethe platform 1 is in any event now wholly supported by the framework 11.The pylons 5 are held in their raised positions with respect to theworking platform 1 by any suitable means, such as by inverting the pawls8 (FIG- URE 5) as previously described.

When the platform assembly has arrived over the site, the pylons 5 arereleased so that they may slide by gravity downwardly through therespective platform openings 4 and tank openings 2a within which theyare situated, and sea water is admitted to the interior of each pylon byopening suitable valves (not shown) thereof, so that each pylon sinks torest at its lower end 5b against the mud bottom 19 of the ocean floor.Of course, during the pylon sinking operation, additional pylon sections5a are attached as needed, and to provide the aforementioned pylonoverheight 36. By their weight the pylons press themselves into the mudbottom 19 until refusal sets up. At this stage in the pylon settingoperation, the previously referred to additional water ballast is pumpedinto each pylon to a height of about 75 feet above sea level, so thatthe weight of this ballast water will be an additional force tending topress the pylon downwardly into the ocean bottom. Of course, uponaddition of such ballast water, each pylon will descend a furtherdistance at this stage of the operation.

The ratchet and pawl arrangements 32 between each pylon 5 and theplatform 1 are then engaged in the manner illustrated by FIGURE 5 and,if not already so attached, the platform 1 is attached to the tankframework 11 by the releasable attachments illustrated in FIG- URE 6.

Sea water is then admitted to the tanks 2 either by pumping of throughvalves (not shown) in each of them, causing them to be rendered lessbuoyant. Thus, all of the pylons are pressed downwardly under a forceequal to the total weight of the tanks 2 and their incidentalsuperstructure framework 11, and by the full weight of the platform 1including all of its equipment load, and also by the weight of thepylons themselves and the referred to overheight of ballast watertherein. This pressing weight is maintained for a period of time untilthe platform assembly, including the pylons 5, has sunken a preselectedunit distance, preferably 12 feet, which is equal to the vertical heightbetween adjacent rungs 7 of the ratchet and pawl arrangements 32 of thepylons. Upon achieving such depth, the water is pumped out of the tanks2 to render them fully fioatable so that they rise, traversing the sameunit distance in upward direction and lifting the platform 1 withrespect to the pylons 5 which remain stationary in view of the automaticreleasing of the attachment between the platform and pylons as iseffected by the ratchet and pawl arrangements 32. When the tanks 2 haveachieved their normal floating elevation, the pawls 8 will engage therespective of the next higher rungs 7 of the ladders 6, whereupon wateris again admitted to the tanks 2 to repeat the pressing operation byapplying their weight, together with the weight of the platform 1, tothe pylons 5.

By repeated alternate partial flooding and emptying of the three buoyanttanks 2 between a freeboard of from 2 feet to 14 feet, the pylons 5 aredepressed 12 feet at a time until their ends 5b meet soil pressureresistance equal to the total pressing weight. At this stage, it may bethat the resistance encountered by any one or two of the pylons may beconsiderably less than that as has been encountered by the remainingpylon or pylons. In these circumstances, it is desirable to press theremaining pylons to the same resistance value. To do so, the ratchet andpawl arrangements 32 at the pylon or pylons which have encountered thegreater resistance are disconnected, and the alternate partial floodingand emptying of the three buoyant tanks 2 is continued so as to exertvirtually the total weight of the tank structure and platform on onlyone or perhaps two of the pylons so as to press it, or them, furtherinto the sub-bottom 20 until acceptable resistance is encountered. Theextent to which all of the tank and platform weight may be transmittedto only one or two pylons is determined by the acceptable bending momentas may be established in the pylon or pylons. However, substantialadditional weight may be so transmitted by, for example, completelyflooding the tank or tanks which are associated with the pylons whichare to be pressed further, thereby providing addition-a1 sea waterballast weight corresponding to any extent of projection of such tank ortanks above sea level, and only partially flooding the remaining tank ortanks in the same or varying degree. It becomes apparent that suchpressing weight might also be applied to each of the pylons in sequenceat this stage of the operation to insure that each of the pylons havereached a depth of penetration in the sub-bottom 20 whereat the soilresistance force is a maximum.

When penetrating the mud layer 19, the pylon pressing operation proceedsrather rapidly at a rate of about 1 foot per minute since, considering aconventional oil drilling platform structure as has been described, theavailable pylon placing pressure is on the order of some 15,000 poundsper square foot through mud soil which is capable of supportingpressures of only about 200 pounds per square foot. The operationproceeds more slowly when the pylons are penetrating the sub-bottom 20which has much greater soil pressure.

In this manner, each pylon may be pressed to refusal by a force (equalto the total weight of the tanks 2 and tank framework 11, the platform1, the pylons 5 themselves, and the weight of the pylon ballast water,as aforesaid) totaling three times the anticipated normal or workingload as will subsequently be exerted thereon by the platform 1. To makethis overload capacity of the pylons available to resist the forces ofwaves and the like during normal drilling operations, the loading of thepylons must be relieved to the same extent.

Accordingly, after all of the pylons have been set as aforesaid, thetanks 2 are again raised so as to position the platform 1 at theultimately desired working platform elevation, and all of the ratchetand pawl arrangements 32 are engaged so as to distribute the platformweight evenly between all of the pylons 5. Additional lateral bracing 37(FIGURE 4) may be attached between the platform and the pylons, ifdesirable. All of the bolt attachments 31 are then released, and thetanks 2 are again flooded so that they sink downwardly along the pylonsto rest against the mud bottom 19 as shown in FIGURE 4. The aforesaidadditional ballast water is emptied from the pylons 5 to relieve theirloading to this extent and, if desired, some of the remaining ballastwater may be pumped from within the pylons to further and commensuratelyrelieve their preloaded condition.

The offshore platform assembly is now ready to serve its purpose as anoil well drilling platform, and, it will be noted from FIGURE 4 that theframework 11, at a location below the platform side out 13, has abracket 21 attached and adapted for receiving the lower portion of theChristmas tree pipe 41 which passes therethrough.

When drilling operations have been completed, the platform assembly isremoved from the drill site by first emptying the water from the tanks 2to cause their travel, under buoyant influence, upwardly along thepylons 5 and to their floating condition in supporting engagement withthe platform 1. The ratchet and pawl arrangements 32 are disconnected bypivoting the pawls 8 against the bias of their springs 10 and holdingthe same out of engagement with the pylon members 6. By pump means (notshown), the pylons are emptied of the water which they contain,whereupon they will rise by buoyancy out of their embedded relation withthe ocean bottom 19, 20. In this connection, and assuming that thepylons are submerged a distance of 300 feet, the buoyant pressureexerted on each pylon is equal to about 9 tons per square foot of pylonarea, or a total buoyant force of some 2800 tons on each pylon whosediameter is 20 feet, which force is ordinarily sufficient to raise thepylon out of the ocean bottom. Of course, and as previously mentioned,the ratchet and pawl arrangements 32 may be reversed, and an additionallifting force imparted by the buoyant tanks 2 might also be utilized toremove the pylons.

As an example of the extent to which the pylons may be preloaded usingthe present invention, it is considered that the weight of the platform1, together with the derrick 12 and other drilling and auxiliaryequipment as may be placed thereon, totals some 2400 tons. The weight ofthe three tanks 2, including their attaching framework 11, totals about1500 tons. Each of the three pylons itself weighs about 300 tons, andthe additional ballast water in each pylon (75 feet in height asaforesaid) adds some 700 tons to the weight of each pylon. As regardsthe additional weight provided by '75 feet of additional ballast waterin each pylon, the 20 foot diameter pylon has an area of about 314square feet, and salt water weigh 64 pounds per cubic foot. The totaladditional load exerted by the 75 feet of ballast water is thereforeequal to 3l4 75 64, or 1,500,000 pounds, i.e. about 700 tons per pylon.Thus, the total pressing load as may be applied to each pylon is about2300 tons, or a pressure of about 7 tons per square foot, when all ofthe pylons are being simultaneously pressed into the ocean bottom. Ofcourse, each pylon may be overloaded independently of the others up toabout 4900 tons. When the tanks 2 have been detached from the platform 1and lie sunken on the ocean floor as shown in FIGURE 4, and after theadditional ballast water has been emptied from each of the pylons, andconsidering that the platform 1 is attached and that each pylon has beenadditionally partially dewatered, the total stationary load exerted byeach pylon on the ocean bottom is reduced to about 1100 tons, or 3 /2tons per square foot. It is therefore apparent that an overload marginof from 1200 to 3800 tons is available at each pylon to resist wave andwind action, unexpected ramming, or the like.

Thus, an offshore platform assembly and a technique for installing andremoving the same has been described which achieves all of the objectsof the invention.

What is claimed is:

1. The method of increasing the available load-resisting capability of aplurality of vertical pylons of an offshore platform assembly whereinthe lower ends of the pylons are embedded in the bearing soil beneath aseaway or the like in which the platform assembly is situated, saidplatform assembly including a horizontal platform disposed at apreselected elevation a substantial distance above sea level and fixedlybut releasably attached to each of said pylons substantially adjacentthe respective upper ends thereof whereby said platform is supported bysaid pylons and may be detached and thereby rendered capable ofvertically slidable movement with respect to all of said pylons, saidpylons being substantially freestanding and unobstructed along theirrespective lengths extending below said platform, said method comprisingthe steps of fixedly attaching to said platform a plurality of heavy butfloatable tanks corresponding in number to said plurality of pylons,said tanks being then in floating condition below said platform andrespectively in substantially surrounding but unattached relation withrespect to each of said pylons, all of said tanks being rigidly attachedtogether, then rendering all of said tanks less buoyant for a period oftime whereby the weight of said tanks together with the weight of saidplatform is exerted on all of said pylons and whereby said tanks andsaid platform and said pylons move downwardly a preselected distanceduring said time period to press said lower ends of the pylons saidpreselected distance into said soil, then detaching said platform fromall of said pylons and rendering all of said tanks more buoyant wherebysaid tanks and platform move upwardly substantially said preselecteddistance with respect to said pylons, thereafter repeating for as manytimes as desired the aforesaid steps of attaching said platform adjacentsaid upper ends of the pylons, rendering said tanks less buoyant for aperiod of time, and detaching said platform from said pylons andrendering said tanks more buoyant, and, after the last said step ofrendering said tanks more buoyant, fixedly attaching said platform toall of said pylons at said preselected elevation of the platform,thereafter detaching all of said tanks from said platform whereby thelatte-r is supported solely by all of said pylons, and then sinking allof said tanks to rest upon said bearing soil while maintaining theirsaid attached together relationship and their said substantiallysurrounding and unattached relation with the respective of said pylons.

2. The method according to claim 1 wherein, after said tanks areattached to said platform and while said platform is situatedsubstantially at its said preselected elevation but prior to the finalstep of fixedly attaching said platform to all of said pylons, saidplatform is attached to a fewer number of said plurality of pylons whilemaintaining said detached relationship of said platform with respect tothe remainder of said plurality of pylons, then all of said tanks arerendered less buoyant for a period of time whereby substantially theweight of all of said tanks together with the weight of said portion isexerted only on said fewer number of pylons to press the lower ends ofsaid fewer number of pylons a distance into said soil, and thereaftersaid platform is detached from said fewer number of pylons and all ofsaid tanks are rendered more buoyant whereby said tanks and saidplatform move upwardly to again dispose said platform substantially atits said preselected elevation.

3. An offshore platform assembly comprising a horizontally disposedworking platform, a plurality of spaced apart and vertically disposedelongated hollow pylons each mounted for vertical slidable movementthrough said platform, releasable connection means between said platformand each of the respective of said pylons, said releasable connectionmeans at each pylon being engageable and disengageable independently ofany other whereby each pylon is independently slidable with respect tosaid platform, a plurality of heavy but floatable hollow and enclosedtanks corresponding in number and respectively surrounding each of saidplurality of pylons, the buoyancy capacity of said tanks being adequateto floata'bly support said assembly, said tanks being disposed belowsaid platform and in unattached and substantially slidable relation withrespect to its associated pylon, a tank superstructure framework rigidlyattaching said tanks together and projecting upwardly from said tanks tosupport said platform at a preselected elevation a substantial distanceabove the normal waterline of said tanks when floatably supporting saidassembly, second releasable connection means between said tanksuperstructure frame work and said platform, said second releasableconnection means when released providing complete detachment of saidsuperstructure from said platform and being operable independently ofany of the first said releasable connection means between said platformand the respective of said pylons, means for introducing and expellingwater into and out from each of said tanks, and means for introducingand expelling water into and out from each of said pylons, said pylonsbeing unobstructed along their respective lengths extending below saidplatform whereby said tanks and superstructure framework are freelyslidable with respect to all of said pylons between said platform andsubstantially the lower ends of said pylons.

4. An offshore platform assembly comprising a horizontally disposed andnon-floatable working platform, pylon support means consisting of threetriangularly spaced apart and vertically disposed elongated hollowpylons each mounted for vertical slidable movement through saidplatform, each said pylon being hollow throughout substantially itsentire length and having a downwardly protruding and spherically shapedclosed lower end, ratchet and pawl connection means between saidplatform and the respective of said pylons for holding said platform andthe respective of said pylons in substantially fixed relation withrespect to each other, said ratchet and pawl means at each pylon beingengageable and disengagea'ble independently of any other, and each saidratchet and pawl means when engaged permitting free upward movement ofsaid platform with respect to its associated pylon but preventing upwardmovement of its said associated pylon with respect to said platform and,when disengaged, permitting upward movement of its said associated pylonwith respect to said platform, three heavy but floatable hollow andenclosed tanks for floating said assembly, said tanks being disposedbelow said platform each in closely surrounding but substantiallyslidable relation with respect to one of said pylons, a tanksuperstructure framework rigidly attaching said tanks together andhaving height to project upwardly of said tanks to the underside of saidplatform to support the latter at an elevation which is a substantialdistance above said tanks, connection means between said tanksuperstructure framework and said platform for holding all of said tanksand said platform in substantially fixed relation with respect to eachother, said connection means including means for releasing saidconnection between said superstructure and said platform and consistingof means providing complete detachment of said tanks and their saidsuperstructure from said platform, said releasing means being operableindependently of any of said ratchet and pawl connection means, meansfor introducing and expelling water into and out from each of saidtanks, and means for introducing and expelling water into and out fromeach of said pylons.

References Cited by the Examiner UNITED STATES PATENTS 201,569 3/1878Striedinger et al. 61-46.5 1,962,428 6/1934 Colbie 6153 X 2,248,051 7/1941 Armstrong 61--46.5 2,589,146 3/ 1952 Samuelson 6146.5 2,603,0687/1952 Wilson 61-46.5 2,614,803 10/1952 Wiggins 6l--46.5 X 2,637,1725/1953 Howard 6l46.5 2,771,747 11/1956 Rechtin 61-46.5 2,946,198 7/1960Knapp 6146.5 3,013,396 12/1961 Suderow 61-465 FOREIGN PATENTS 606,033 8/1948 Great Britain. 713,298 8/1954 Great Britain.

EARL I. WITMER, Primary Examiner.

3. AN OFFSHORE PLATFORM ASSEMBLY COMPRISING A HORIZONTALLY DISPOSEDWORKING PLATFORM, A PLURALITY OF SPACED APART AND VERTICALLY DISPOSEDELONGATED HOLLOW PYLONS EACH MOUNTED FOR VERTICAL SLIDABLE MOVEMENTTHROUGH SAID PLATFROM, RELEASABLE CONNECTION MEANS BETWEEN SAID PLATFORMAND EACH OF THE RESPECTIVE OF SAID PYLONS, SAID RELEASABLE CONNECTIONMEANS AT EACH PYLON BEING ENGAGEABLE AND DISENGAGEABLE INDEPENDENTLY OFANY OTHER WHEREBY EACH PYLON IS INDEPENDENTLY SLIDABLE WITH RESPECT TOSAID PLATFORM, A PLURALITY OF HEAVY BUT FLOATABLE HOLLOW AND ENCLOSEDTANKS CORRESPONDING IN NUMBER AND RESPECTIVELY SURROUNDING EACH OF THESAID PLURALITY OF PYLONS, THE BUOYANCY CAPACITY OF SAID TANKS BEINGADEQUATE TO FLOATABLY SUPPORT SAID ASSEMBLY, SAID TANKS BEING DISPOSEDBELOW SAID PLATFORM AND IN UNATTACHED AND SUBSTANTIALLY SLIDABLERELATION WITH RESPECT TO ITS ASSOCIATED PYLON, A TANK SUPERSTRUCTUREFRAMEWORK RIGIDLY ATTACHING SAID TANKS TOGETHER AND PROJECTING UPWARDLYFROM SAID TANKS TO SUPPORT SAID PLATFROM AT A PRESELECTED ELEVATION ASUBSTANTIAL DISTANCE ABOVE THE NORMAL WATERLINE OF SAID TANKS WHENFLOATABLY SUPPORTING SAID ASSEMBLY, SECOND RELEASABLE CONNECTION MEANSBETWEEN SAID TANK SUPERSTRUCTURE FRAMEWORK AND SAID PLATFORM, SAIDSECOND RELEASABLE CONNECTION MEANS WHEN RELEASED PORVIDING COMPLETEDETACHMENT OF SAID SUPERSTRUCTURE FROM SAID PLATFROM AND BEING OPERABLEINDEPENDENTLY OF ANY OF THE FIRST SAID RELEASABLE CONNECTION MEANSBETWEEN SAID PLATFORM AND THE RESPECTIVE OF SAID PYLONS, MEANS FORINTRODUCING AND EXPELLING WATER INTO AND OUT FROM EACH OF SAID TANKS,AND MEANS FOR INTRODUCING AND EXPELLING WATER INTO AND OUT FROM EACH OFSAID PYLONS, SAID PYLONS BEING UNOBSTRUCTED ALONG THEIR RESPECTIVELENGTHS EXTENDING BELOW SAID PLATFORM WHEREBY SAID TANKS ANDSUPERSTRUCTURE FRAMEWORK ARE FREELY SLIDABLE WITH RESPECT TO ALL OF SAIDPYLONS BETWEEN SAID PLATFORM AND SUBSTANTIALLY THE LOWER ENDS OF SAIDPYLONS.